The bicycle is currently one of the most efficient means of human powered transportation in terms of converting human power into distance traveled. Modern bicycles require approximately 150 watts (0.2 HP) for consistent travel of approximately 15 MPH on level ground and less than 30 watts (0.04 HP) for travel at 5 MPH. This efficiency has been slowly improving throughout the history of the bicycle through engineering refinement; for example gearing, weight reduction, ergonomic/biometric alterations, and reduced mechanical and tire friction.
This invention relates generally to the field of bicycles and electric-assist powered bicycle. Bicycles being a very efficient form of human-powered two-wheeled transportation, and electric-assist bicycles being bicycles with supplemental force to accommodate the limitations of stamina and power inherent in a human-only powered bicycle system.
While bicycles have evolved to be a very efficient form of human-powered transportation, human power ultimately remains the primary restriction to increased utility of the bicycle as a general transportation device. There are two primary shortcomings in a human-powered system. First, human beings can typically generate only 100–200 watts of power for an extended time period (e.g., 15 minutes); the power output and length of time vary significantly from person to person. The second shortcoming is that humans have a limited amount of power they can produce; even the fittest persons can only generate approximately 500 w of burst energy.
The practical results of these performance limitations become obvious when looking at the power requirements for bicycling at higher speeds and/or traveling up grades. In order to travel on level ground at speeds of 20, 25, and 30 MPH, the power requirements in watts respectively are 260, 430, and 670. Obviously, constant travel at any speed greater than 20 MPH is impossible for all but the fittest of persons.
Similarly, the same human performance limitations affect travel on grades. At a constant 15 MPH, grades of 2, 5, and 10 percent result in power requirements of 275, 470, and 780 watts respectively. Even traveling up a grade of 10 percent at 5 MPH requires 240 watts; a grade of 20 percent results in a requirement of 450 watts.
Thus, regardless of the efficiency of modern bicycles, the utility of a bicycle is seriously limited by the stamina and power of the human operator and thus generally uncompetitive with motored forms of transportation in terms of speed and traveling distance. One solution to the limited utility of bicycles has been to add some type of power assistance to the standard bicycle. Numerous inventions have focused on a means by which to accomplish this, whether by electricity or other methods. Such systems add significant utility to the standard bicycle since the combined human and artificial power output increases range and total power output significantly; adding only ½ horsepower of continuous output to a bicycle has a significant impact on performance. For example, a ½ horsepower increase on a 5 percent grade results in a continuous speed increase from 5 MPH to nearly 18 MPH.
However, designing a practical electric propulsion system for a bicycle has proven to be a formidable task as evidenced by the absence of such electric powered vehicles currently available. Inventions related to motor assisted bicycles go back to the early 20th century (e.g., U.S. Pat. Nos. 1,158,311; 2,080,972, and 2,586,082) and typically added a cumbersome gas powered motor with a “friction drive” (i.e. a powered roller applying force directly to the tire of the bicycle).
There are also a number of more contemporary inventions that attach electrical components such as batteries, motor controllers and electric motors to a conventional bicycle (e.g., U.S. Pat. Nos. 3,841,428; 3,878,910; 3,905,442; 3,912,039; 3,921,745; 3,966,007; 4,516,647; 5,316,101; 5,491,390; 5,778,998; 5,857,537; 5,865,267; 5,910,714; 6,011,366; 6,516,911; U.S. Published Pat. App. 2002/0027026; Japanese Pat. No. 09175472A). The majority of these inventions use simple but inefficient friction drives to provide power to one wheel of the bicycle. Additionally these inventions do not typically support quick removal of the propulsion system. Another patent discloses a friction based drive mechanism but claims to be easily detachable (U.S. Pat. No. 3,841,428); this design uses a lever extending to a point near the leg of the operator that allows the operator to both control the level of friction and control the output of the motor.
One invention avoids the use of a friction drive by connecting the motor and rear wheel via a drive shaft extending from an electric motor above the rear wheel to a final bevel drive attached to the rear axle (U.S. Pat. No. 5,487,442). A similar disclosure specifies one embodiment that uses a chain drive from a motor above the rear wheel to the rear wheel (German Pat. No. DE3213043). Still other systems use a standard bicycle frame with battery placed at some point in the forward triangle and an exposed motor driving either the rear hub, primary drive chain, or crank (U.S. Pat. Nos. 3,915,250; 4,085,814; 4,122,907; 4,871,042; 5,433,284)
Still other related inventions have chosen to add electric propulsion to a non-standard bicycle frame and/or use significant non-standard bicycle componentry (U.S. Pat. Nos. 4,030,562; 4,168,758; 4,280,581; 4,410,060; 4,541,500; 5,474,148; 5,853,062; 6,131,683; 6,155,369; D473,495S) or house the electric propulsion system in a completely auxiliary fashion (e.g., U.S. Pat. No. 6,290,014). Two British patents/applications also disclose non-friction drive systems.
The first (UK Pat. No. GB2249529) uses a small electric motor driving the primary crank, while the battery is located on the left-hand side of the bicycle at the rear. The second (UK Pat. Publication No. GB2262490) uses a battery and motor module attached to the rear triangle of the bicycle frame at about the level of the top of the rear wheel. The battery alone is stated as easily detachable, and is very small, with very little battery capacity. The entire unit is “permanently affixed to the body except for repair purposes”. A similar device (U.S. Pat. No. 6,290,014) uses a motor integrated with the crank and places the batteries in a rack over the rear wheel. Such devices are not easily and conveniently removed from the bicycle, place the weight of the unit too high on the bicycle, and do not adapt to full-suspension bicycles.
Two previous disclosures embody the general concept and layout of the current invention (U.S. Pat. Nos. 5,816,355 and 5,842,535) in that they both house electric propulsion system components in enclosures. However, both of these inventions rely on an inefficient friction drive wheel contacting the rear wheel of the bicycle, result in a relatively high center of gravity due to the location of weight on the bicycle frame, fail to make provisions for operation with a rear suspension bicycle, and do not provide additional storage. Further, each inconveniently requires manual disengagement of the drive wheel in order to reduce motor drag when power assist is not required.
It is the objective of the present invention to provide an improved electric-assist bicycle system that overcomes or greatly reduces the inherent compromises of existing designs. This invention embodies the advantages of current inventions (e.g., improved power and endurance, human and motor working parallel power), while circumventing common disadvantages. Improvements in the present invention include a system in which the integrity and efficiency of the stand-alone bicycle, with all its evolutionary improvements, is maintained. For example, the bicycle of this invention includes complete gear sets for efficiency and conventional construction and components, and is lightweight and has a normal outward appearance. Yet it is also the objective of this invention to provide an electric-assist method that provides clear advantages over other stand-alone bicycles and other electric-assist bicycles. The present invention provides sophisticated and efficient drive system embodiments afforded by a linkage from the motor to the rear wheel; not to the tire as with “friction drive” systems with their inherent transfer inefficiency, moisture intolerance, and issues with limited tire selection and increased tire wear. This invention also supports sufficient storage capacity to carry an energy supply consistent with the rider's needs. Further, this invention uniquely has a drive system that is compatible with suspended rear wheel motion, yet maintains suspension efficiency by placing the motor in a suspended element of the bicycle, while placing the weight of the motor drive system at a low level. It is also the objective of this invention that the complete system is transformed from an efficient and normal appearing stand-alone bicycle to a capable electric-assist vehicle in less than one minute and without tools. Further, these critical components are packaged in a way that maintains pleasing aesthetics, provides a safe enclosure for vulnerable electric components, is easily transportable, and adds additional utility to an electric assist bicycle system above that afforded by prior inventions.